Single‐molecule detection of thionine on aggregated gold nanoparticles by surface enhanced Raman scattering

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Abstract
We report observations of single‐molecule detection of thionine and its dynamic interactions on aggregated gold nanoparticle clusters using surface enhanced Raman scattering (SERS). Spectral intensities were found to be independent of the size of Au nanoparticles studied (from 17 to 80 nm) at thionine concentration below 10−12 M or at single‐molecule concentration levels. Raman line separations and, in particular, spectral fluctuations and blinking were also observed, suggesting temporal changes in single molecular motion and/or arrangements of thionine on Au nanoparticle surfaces. In contrast, by using dispersed Au nanoparticles, only ensemble SERS spectra could be observed at relatively high concentrations (> 10−8 M thionine), and spectral intensities varied with the size of Au nanoparticles. Copyright © 2007 John Wiley & Sons, Ltd.